SOLUTION FOR FIXING AND PROTECTING PERMANENT MAGNETS IN BRUSHLESS MOTORS
In recent years, the field of electric motors has witnessed exponential growth in the use of BLDC brushless motors, due to the many advantages they offer, including the fact that these motors are smaller in size while delivering the same torque, they consume less electricity, have higher speeds, require less maintenance, dissipate heat better and can be overloaded.
One of the most critical issues with this type of SPM (Surface permanent magnets) motor is the complexity of attaching the magnets to the rotor, since they cannot be welded to it because of their fragility and because at high temperatures permanent magnets suffer an irreversible loss of magnetic flux (Curie point).
REVOLUTIONARY SOLUTION POLITUBES COVERED BY EUROPEAN INDUSTRIAL PATENT NO. EP2763283B1
To overcome this problem Politubes, in conjunction with DuPont, has developed a special spiral-wound tube made of heat-shrinkable polyester (Mylar HS), which enables automated fixing of permanent magnets, thereby reducing the cost of assembling these motors.
The spiral-wound tube is fitted onto the rotor with the magnets in position and is then instantly heat-shrunk, resulting in a firm attachment of the magnets to the rotor, protection for the magnets from scratches, abrasions and polluting agents and no danger of cracking or damage to the delicate permanent magnets during the assembly process.
The temperatures used for heat-shrinking are well below the Curie point, and therefore three is no risk of reducing the magnetic flux of the magnets.
Our heat shrinkable polyester tubing also guarantees the double electrical insulation requested by IEC 60335-1-2 standard, allowing brushless motor manufacturers to obtain VDE / UL / CCC certificates.
The reinforced insulation of the BLDC motor obtained thanks to the use of our tubes, meets the strictest standards IEC 60335-1-2 because it guarantees:
- The double electrical insulation (4 – 7 kV) required inside the brushless motor, avoiding the use of grounding connections.
- A thermal insulation (class B-F) as it can be used at temperatures with peaks up to 150 – 155 ° C.
Other important advantages offered by the heat-shrinkable tubes include:
- Unlike very expensive steel rings, the spiral-wound tube also wraps around and protects the ends of the magnets, which are also subject to corrosion and which, if chipped, can cause the motor to seize.
- The trimming that often has to be done during the assembly process when using rigid rings is avoided; the Politubes spiral-wound tube adheres perfectly to the magnets, taking their shape and protecting them from cracking and scratching.
- Balancing of the rotor: If the magnets are glued in place on the rotor there can be some issues with the balance of the rotor depending on the amount of glue used for each magnet. This means to put in place some complicate system to balance the rotor contributing to increase the scrap rate. With our round heat shrink tubes the rotor balancing is easily obtained as well reducing the production scrap rate.
- Part of the assembly process is removed, since potentially costly and often manual bandage with tape impregnated with epoxy resins can be eliminated; this avoids as well slow resin activation time in oven; productivity is thereby increased and hidden production costs reduced.
- The tubes can also be used successfully in combination with the epoxy glues used to fix the magnets, guaranteeing additional protection against the potential failure of the glue and detachment of the magnets, and against scratches or other polluting agents.
- The minimum dimensions are between 0.12 and 0.2 mm; this avoids any reduction in the magnetic flux of the rotor, and allows the magnets to achieve maximum performance.
In motors that use annular magnets produced by the compression molding of Nd-Fe-B Neodymium Iron Boron magnets with the addition of thermosetting resins (plastoferrite), our tube also protects the magnet from corrosion, given the fragility of the alloys used, thereby preventing the motor from seizing.
The adhesives used, which have been carefully selected over forty years of experience, comply with all REACH and RoHS standards and ensure that the films used fully retain their original properties.
Politubes has established some important partnerships with manufacturers of automatic machines that guarantee the correct heat shrink process of our tubes. These companies can help you achieve a fully automatic and highly efficient production line.
The Politubes R&D center remains at your disposal should you require anything, and to work together to design tailored, innovative solutions.
Download the DuPont-Politubes Case History